Method for producing seams on webbings for technical purposes

ABSTRACT

In a method for producing seams on webbings for technical purposes, in particular on lifting straps or lashing straps for securing cargo during transport, a sewing thread is used to produce the seam, the fine strength of said sewing thread being significantly greater than the fine strength of the fibrous material or yam from which the webbing is produced. In this way, the binding load of a webbing having a seam is increased.

This invention relates to a method for producing seams on webbings fortechnical purposes, more particularly on lifting belts or lashing strapsfor cargo securement in transit.

Webbings for technical purposes are generally produced from yarns formedfrom manufactured fibers. The usual choice is for filament yarnscomposed of polyamide (PA 66), polyester (PES) or polypropylene (PP)which are heat stabilized and light- and aging-resistant and which havea tenacity of at least 60 cN/tex. Connection points, for example at endloops to enclose fitting parts, are stitched by using multiplelongitudinal and/or transverse seams to connect together a sheetlikeportion in which the webbing parts to be connected together lie on topof each other. The sewing yarn used for this is typically made of thesame fiber material as the webbing in order to ensure the same physicaland chemical stability. In fact, for particularly demandingapplications, such as lifting belts for example, the same tenacity isprescribed for the webbing material and the sewing yarn.

Tensile tests on webbings with seams have shown that the loading limitis determined by the breaking load of the seam, since it is appreciablysmaller than the breaking load of the webbings.

It is an object of the present invention to provide a method forproducing seams on webbings which provides an increase in the strengthand hence the breaking load of the seam.

I have found that this object is achieved according to the presentinvention by producing the seam using a sewing yarn having a tenacitywhich is appreciably greater than the tenacity of the fiber material oryarn of which the webbing is made.

The invention is based on the insight that using sewing yarn having atenacity which is significantly higher, for example twice as high, thanthe tenacity of the yarn of the webbing provides a significant increasein the load-bearing capacity of the seam, effectively also significantlyincreasing the loading limit for the webbing provided with seams. It hasfurther been found that the significantly higher tenacity of the sewingyarn has no adverse effects on the strength and also the remainingperformance characteristics of the webbing. Tests have further shownthat the use of sewing yarn of particularly high tenacity compared withthe tenacity of the webbing yarn provides a seam strength which is equalto or greater than the strength of the webbing.

Particularly favorable results in the case of polyester webbings wereobtained with a sewing yarn consisting of Dyneema fiber material.Dyneema fiber material is a fiber material of high tensile strength,which includes highly oriented fibers composed of high molar mass linearpolyethylene. High molar mass here is to be understood as an averagemolar mass of at least 400 000 g per mole. Linear polyethylene is to beunderstood as meaning polyethylene having less than one side chain per100 carbon atoms, preferably less than one side chain per 300 carbonatoms. The polyethylene may additionally contain up to 5 mol % of one ormore other alkenes copolymerizable therewith, such as propylene, butene,pentene, 4-methylpentene, octane.

It is particularly advantageous when the sewing yarn is made ofpolyethylene fibers consisting of filaments obtained in a gel-spinningprocess as described in GB-A-2042414 and in GB-A-2051667 for example.This process comprises essentially preparing a solution of a polyolefinof high intrinsic viscosity, spinning the solution into filaments at atemperature above the dissolving temperature, cooling the filaments tobelow the temperature at which the gel state is attained, and stretchingthe filaments before, during or after removing the solvent.

To evidence the attainable strength of a seam produced by the method ofthe present invention on a webbing of polyester multifil yarn having atenacity of at least 60 cN/tex for the fibers, a thickness of 1.8 mm anda width of 45 mm, the webbing was formed into a loop and the freewebbing end of the loop was stitched to the webbing along a length of 80mm, using seams extending in a zigzag pattern at an angle to thelongitudinal direction of the webbing. The sewing yarn used was, in thecase of a first sample, polyester multifil yarn having a tenacity of 60cN/tex and, in the case of a second sample, yarn formed from fibersbearing the trade name Dyneema from DSM High Performance Fibers B.V.having a tenacity of 236 cN/tex. The subsequent tensile tests revealed abreaking load of 19 602 N for the first sample and of 27 291 N for thesecond sample.

Two further tests were performed using the same webbing and the samesewing yarns, except that the loop was stitched to the webbing onlyalong a length of 40 mm using 12 zigzag seams. In this case, thebreaking load was 24 226 N in the case of the sample stitched with thepolyester sewing yarn and 28 647 N in the case of the sample stitchedwith Dyneema sewing yarn.

The results show that breaking load of seams on webbings can beincreased appreciably provided that, in accordance with the presentinvention, the seams consist of a sewing yarn having a tenacity that ismultiple times higher than that of the webbing yarn. The load-bearingcapacity of the webbing is better utilized as a result. Accordingly,thinner and hence lighter webbings can be used for given load scenarios.

1. A method for producing seams on webbings for technical purposes,characterized in that the stitching is effected using a sewing yarnhaving a tenacity which is significantly greater than the tenacity ofthe fiber material of which the webbing is made, more particularly is atleast twice the tenacity of the fiber material of which the webbing ismade.
 2. The method according to claim 1, characterized in that thetenacity of the sewing yarn is at least four times the tenacity of thefiber material of the webbing.
 3. The method according to either of thepreceding claims, characterized in that the sewing yarn consists ofhighly oriented fibers composed of high molar mass linear polyethylene.